Table – Alternate Codes Map

The handling of alternate codes (formally known as associated codes) will be handled differently in the new table model.  In the current table model, each code in its expression information structure contained a single array of associated codes along with a count and an index to a second set of associated codes within the array.  In the new table model, these will be removed from the expression information structure.

The new table model will contain the information for a code in a single table entry instance, which will be handled by a pointer.  The table class will contain some static data members (members shared by all instances).  The alternate code information will be stored in one of these new static data members, specifically a map from a primary code table entry pointer (the key) to its alternate codes (the value).

The value of this alternate map will contain an array (a standard array will be used) of three elements.  Each element represents the alternate codes for a particular operand.  Generally, the first element (index of 0) will have alternate codes where the data type of the first operand is different from the primary code.  The second element will have alternate codes where the data type of the second operand is different from the primary code.  This was roughly the purpose of the second associated codes.

The third element of the array is applicable only for three argument internal functions, which is new.  There are currently no planned internal functions that have different data types in the third argument.  This third element will be used to associate three argument functions to there primary code with two arguments.  This applies to the MID$ and INSTR functions which have two and three argument versions.  This similarly applies to the ASC function, but its second form has two arguments, so the second element of the array is used.

Each element of this array will contain a vector of alternate code table entry pointers.  A particular element may have an empty vector indicating no alternate codes with different data types for that operand or argument.  The first step will be to automatically generate this map from operator and internal function table entries from the operand data type information.